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Updated repost of The Fallacy Fork and the Limits of Logic, at 3 Quarks Daily

No quiet moment; Theresa May calls snap UK election (BBC)

I had been waiting for a quiet moment to write about this, but there isn’t going to be a quiet moment, so now will have to do. [Update: these words went up on 3 Quarks Daily last Monday. On the Tuesday, Theresa May called a snap UK General election]

Debaters regularly accuse their opponents of using fallacies. These can be formal fallacies, such as simple errors of logic, or informal fallacies, such as appeal to authority, ad hominem and strawman arguments, among others. If a piece of reasoning depends on any of these fallacies, so it is claimed, the conclusion does not really follow from the premises, and while it might still be true we have not been given any good reason to believe it.1 And so books that discuss logic, and science-promoting blogs (including one I follow), regularly include descriptions of informal fallacies, with stern instructions to avoid committing them.

Sagan warns us against fallacies. But is exposing fallacies enough to shield us from the demons?

In an article entitled The Fake, the Flimsy, and the Fallacious: Demarcating Arguments in Real Life, Maarten Boudry, Fabio Paglieri and Massimo Pigliucci (henceforth BPP) challenge this view. BPP is written for the perusal of trained philosophers, which I am not, but I use it here as a jumping off point, while mixing in further content of my own. (For a discussion by one of the original authors, see here.)

BPP apply what they call the fallacy fork test to accusations of informal fallacy; either the reasoning is obviously erroneous, in which case no one would really use it, or else it is not obviously erroneous in context, and we still have all the work to do. In the first case, formal analysis is redundant; in the second, the facts of the matter need further consideration. Read the rest of this entry →